Comminuting particles

ABSTRACT

A centrifugal impact mill is provided with a rotor having two radial plates and directs the material to be comminuted radially between the plates onto a coaxial impact track. The particles then pass to either side of the impact track and are propelled through annular sieve tracks arranged on each side of the impact track. The impact track and the sieve tracks can be stationary or arranged to rotate as an outer rotor.

1 Aug. 15, 1972 United States Patent Pallmann 4/1867 Fields 3/1884 Chichester...............24l/7l X 8/1908 .241/71 Thomson...................

Primary Examiner-Granvi11e Y. Custer, Jr. Attorney-Holman & Stern [22] Filed: Feb. 2, 1970 Appl. No.: 7,838

[57] ABSTRACT. A centrifugal impact mill is provided withva rotor having two radial plates and directs the material to be .241/73, 24l/79.3, 241/275 .B02c 13/09 [52] [51] Int.

27 9 70 ,7 3 u. 79 ,6 H 4 Q, m2 M 21 4 2 [58] Field of Search........

comminuted radially between the plates onto a coaxial impact track. The particles then pass to either side of References Cited UNITED STATES PATENTS the impact track and are propelled through annular sieve tracks arranged on each side of the impact track. The impact track and the sieve tracks can be stationamm u mm. In! m un 0 ma m 3 m m mC 7 g m m r 0 Y r 555 77 Una 11.2 44" 2 2,656,988 2,981,490 4/1961 Conley.................;... 2,798,674 7/1957 Dennlng lfllllllllllllllll PATENTEUAUB I 5 I972 SHEET 1 OF 2 Fig. I

PATENTEUAUB l 5 I972 SHEET 2 0F 2 INVENTOR. Mil/Hm PA 4.4 A 1 Arias/(Java COMMINUTING PARTICLES BACKGROUND OF THE INVENTION The present invention relates to apparatus and methods for impact milling, and more particularly to the milling of various different types of materials in the medium and sign particle size ranges.

The invention is, in particular, concerned with fine impact centrifugal mills provided with an interior impact impellor and a coaxial surrounding impact track, with a gap being left between the impact track and the impact impellor. However, the impact track may also be stationary. In those cases in which the impact track rotates, the rotation can be in the same direction as that of the impact impellor, or it can be in the opposite direction. Means may be provided for varying the speed of rotation of the impact impellor'and the impact track independently of one another so that there is a wide range of milling possibilities whereby a large number of different milling specifications can be complied with. The material may simply be fractured or, in the case of fibrous material, the material can be broken down into the individual fibers.

It has been found that with known centrifugal impact mills, the material comminuted is drawn excessively rapidly out through the gap between the impact impellor and the surrounding impact track made up of sieve elements so that there is, on the one hand, an insufficient degree of comminution and, on the .other hand, an uneven and pronounced wear of the sieve surfaces.

SUMMARY OF THE INVENTION The present inventionconsists in a method of comminuting particles in which'the particles are centrifugally thrown radially outwardly against an at least part cylindrical impact track and then pass to both sides of the track with an axial component of movement and pass through a sieve in a centrifugally induced current of gas.

The present invention also consists in a centrifugal impact mill comprising an impact impellor journalled for rotation in a housing, the impellor being defined by two radially arranged plates defining therebetween a gap for the propulsion of material to be comminuted centrifugally in an outward direction, an impact track arranged around the impact impellor and having a width substantially equal to the axial distance between the plates, and preferably, sieve tracks arranged on both sides of the impact track for the outward passage of the material after it has struck the impact track, with the plates being aligned with the sides of the impact track.

The impact track and the sieve tracks on each side thereof can be arranged to rotate in the form of part of an outer rotor or can be arranged stationarily.

It is found that with the centrifugal propulsion of the particles in radial planes towards the impact track, there is provided a very intensive comminution of the material. Further comminution is achieved by the propulsion of the particles in the air current to the sieve tracks, although the wear of the 'sieve is reduced in comparison with known comminuting apparatus. There is no need for the axial width of the track against which the particles are centrifugally thrown by the impellor to be wider than is necessary for a given mill throughput. Since the material is not drawn out to one side of the impact track but to both sides thereof, a loosening and removal of the sufficiently milled material is ensured.

Two embodiments of a mill in accordance with the invention are now described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in cross section and partly in elevation of a centrifugal impact mill in accordance with the invention,

FIG. 2 is a view taken along the line I-lI of FIG. 3, the view looking in'the direction of the arrows, of a further embodiment of the invention, and

FIG. 3 is a view taken along the line Ill-V of FIG. 2, the view looking in the direction of the arrows.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 it can be seen that the mill comprises a mill housing 1 in which an impact impellor 2 is mounted on a shaft 3 in a fixed manner so that the impellor can rotate about a horizontal axis. The impellor is separated radially by a clearance or gap 4 from an impact track denoted generally 5 and the track extends completely around the impellor. The impact track is mounted in a stationary manner in the housing 1 but can easily be replaced.

The impact track 5 comprises grooved plates 6 and lateral radially extending annular partitions 7. The grooves in the plates 6 can, for example, be straight, oblique or herringbone in order to retain the material to be milled in the clearance or gap 4. The clearance between the diameter of the partitions 7 and the diameter of the impact impellor 2 determines the side dimensions of the gap 4. A first plate 8 of the impact impellor 2 is spaced from an opposite second plate or ring 9 arranged in parallelism thereto by a distance equal to the width of the grooved plates 6 of the impact track. The plates 8 and 9 are connected by impellor or impact plates 10, and the plates 10 are provided with beating rails at their outer edge.

The material to be milled or comminuted flows to the impellor 2 through a large cross section inlet duct 11 and is moved in the direction of arrows l2 and 13. The inlet duct is attached to a large housing lid or cover 14 carried on hinges (not shown) and the lid is capable of being opened and closed.

The inlet duct distributes the material over the whole interior width, as indicated by arrow 15, of the impact impellor. The impellor can be provided with internal step structures familiar to those in the art, not shown in the drawing. The width 15 corresponds to the breadth, that is to say the axial dimension of the grooved plates 6. Barrier strips such as 16 can be arranged in the inlet duct in order to reduce the centrifugal suction effect produced by the mill on the material flowing through the inlet duct. Different sizes of strips can be used in accordance with the barrier effect to be obtained. The material to be milled is thrown in the direction of arrow 17 in accordance with the suction effect of the mill and strikes against the impact track 5 over the whole width of the track. This results in an intensive comminution of the material.

To the left and the right of the impact track, there are provided sieve tracks 18, which are limited along their edges remote from the impact track by partitions 19 having apertures 19a in their radially inner parts 19b. The radially inner parts of the partitions are separated from the radially outer parts in order to facilitate dismounting the impact track. The radially inner parts of the partitions are fixed respectively to the lid 14 and the bottom part of the apparatus.

The suction effect produced, in operation, by the impact impellor 2 conveys the sufficiently comminuted material fed into the apparatus from the gap 4 to the left and right, that is to say in the directions denoted by arrows 20 and 21. Additionally, the suction effect propels a part of the entrained material through the sieve tracks 18 in the direction of arrow 22. The finest part of the material which has been comminuted passes in the direction as indicated by arrow 23 through the aperture 19a in the partitions l9 and thereafter the material moves in the direction indicated by arrow 24. The material can thus be classified in-accordance with the type of sieve used.

In the further form of the invention shown in FIGS. 2 and 3 the impact track and the sieve tracks are arranged for rotation and there is a duct connection for the exit or discharge of the material pneumatically.

The housing of a mill or milling apparatus 25 (see in particular FIG. 2) is closed by means of a lid or cover 26 whichcarries an inlet duct or connection 27. On a hollow shaft 28 an outer rotor 29 is mounted within the housing while an impact impellor or interior rotor 31, within the outer rotor, is mounted on a main shaft 30 journalled within the hollow shaft 28. The hollow shaft 28, the main shaft 30, the outer rotor 29 and the impact impellor 31 all rotate in the same or opposite direction, with arrows 34 and 35 in FIG. 3 indicating opposite rotation. The outer rotor 29 comprises two outer ring parts including two sieve tracks 32 with grooved plates 33 therebetween.

The sieve elements of the sieve tracks 32 and shape and type of grooving of the groove plates 33 respective ly can be changed in accordance with the type of material to be milled or handled. It is also possible to change the shape of the sieve tracks which are preferably so arranged that there is a gap 37 between such tracks and beating wing portions 36of the impact impellor 31. The size of the gap influences the degree of comminution of the material milled. In order to increase the centrifugal suction effect, air and material outer rotor while being propelled by the blades 38, in the direction of arrow 46, and flows without being deposited,.in the direction of arrows 43 and 44 to an outlet duct 45. If the apparatus is not provided with the outlet duct 45 but instead is equipped, for example, Wl an outlet extending over the whole clearance width of the housing, the completely ground material falls in the direction of arrow 46 downwardly.

I claim:

1. A centrifugal impact mill comprising a housing, an impact impellor journalled for rotation in the housing, the impellor including two radially arranged plates, said plates defining therebetween, a gap for the propulsion of material to be comminuted centrifugally in an outward direction, said plates having an outer perimeter provided with a plurality of spaced apart impact plates connected thereto and extending substantially normal to the plates, each impact plate having a wing portion at each end extending beyond the associated radially arranged plate, an impact track arranged around the impact impellor, said impact track having a width substantially equal to the axial distance between the plates propelling blades 38 can be arranged as part of the the sieve tracks right to the two sieve tracks 32 of the outer rotor. On passing through the annular sieve tracks, the material is reduced to the desired degree of fineness. It leaves the and sieve tracks arranged on both sides of the impact track for the outward passage of material after the material has struck the impact track, the wing portions of the impact plates extending over the sieve tracksand being spaced therefrom by a small gap whereby there is obtained not only an impact comminution but also a comminution by means of rubbing, pressing, and the like.

2. The centrifugal impact mill in accordance with claim 1, comprising partitions of annular shape adjacent to annular edges of the sieve tracks remote from the impact track, and said partitions having apertures for the passage of milled material.

3. The centrifugal impact mill in accordance with claim 2, in which the partitions include radially inner and radially outer parts, said apertures being in the radially inner part, and the radially inner parts being continued as cylindrical extensions connected with the housing.

4. The centrifugal impact mill in accordance with claim 1, comprising an outer rotor arranged to rotate about the same axis as the impact impellor and including the sieve tracks and the impact track.

5. The centrifugal impact mill in accordance with claim 3, in which the impact track includes impact plate elements which can be replaced with elements of different internal curvature for varying the gap between them and the impact impellor.

6. The centrifugal impact mill in accordance with claim 5, in which the sieve tracks can be exchanged for different types of sieve tracks for different milling specifications.

7. The centrifugal impact mill in accordance with claim 6, comprising an inlet duct connected with an eccentric opening in a plate concentrically arranged within one of said plates of the impellor and said plate being of annular shape. 

1. A centrifugal impact mill comprising a housing, an impact impellor journalled for rotation in the housing, the impellor including two radially arranged plates, said plates defining therebetween, a gap for the propulsion of material to be comminuted centrifugally in an outward direction, said plates having an outer perimeter provided with a plurality of spaced apart impact plates connected thereto and extending substantially normal to the plates, each impact plate having a wing portion at each end extending beyond the associated radially arranged plate, an impact track arranged around the impact impellor, said impact track having a width substantially equal to the axial distance between the plates and sieve tracks arranged on both sides of the impact track for the outward passage of material after the material has struck the impact track, the wing portions of the impact plates extending over the sieve tracks and being spaced therefrom by a small gap whereby there is obtained not only an impact comminution but also a comminution by means of rubbing, pressing, and the like.
 2. The centrifugal impact mill in accordance with claim 1, comprising partitions of annular shape adjacent to annular edges of the sieve tracks remote from the impact track, and said partitions having apertures for the passage of milled material.
 3. The centrifugal impact mill in accordance with claim 2, in which the partitions include radially inner and radially outer parts, said apertures being in the radially inner part, and the radially inner parts being continued as cylindrical extensions connected with the housing.
 4. The centrifugal impact mill in accordance with claim 1, comprising an outer rotor arranged to rotate about the same axis as the impact impellor and including the sieve tracks and the impact track.
 5. The centrifugal impact mill in accordance with claim 3, in which the impact track includes impact plate elements which can be replaced with elements of different internal curvature for varying the gap between them and the impact impellor.
 6. The centrifugal impact mill in accordance with claim 5, in which the sieve tracks can be exchanged for different types of sieve tracks for different milling specifications.
 7. The centrifugal impact mill in accordance with claim 6, comprising an inlet duct connected with an eccentric opening in a plate concentrically arranged within one of said plates of the impellor and said plate being of annular shape. 